1. Field of the Invention
The present invention relates to fabrics employed in web forming equipment, such as papermaking and non-woven web forming equipment, and, more particularly, to forming fabrics in web forming equipment; most preferably in papermaking machines.
2. Description of the Related Art
Paper is conventionally manufactured by conveying a paper furnish, usually consisting of an initial slurry of cellulose fibers, on a forming fabric or between two forming fabrics in a forming section, the nascent sheet then is passed through a pressing section and ultimately through a drying section of a papermaking machine. In the case of standard tissue paper machines, the paper web is transferred from the press fabric to a Yankee dryer cylinder and then creped.
Papermachine fabric is essentially employed to carry the paper web through these various stages of the papermaking machine. In the forming section the fibrous furnish is wet-laid onto a moving forming wire and water is encouraged to drain from it by way of suction boxes and foils. The paper web is then transferred to a press fabric that conveys it through the pressing section, where it usually passes through a series of pressure nips formed by rotating cylindrical press rolls. Water is squeezed from the paper web and into the press fabric as the web and fabric pass through the nip together. In the final stage, the paper web is transferred either to a Yankee dryer, in the case of tissue paper manufacture, or to a set of drying cylinders upon which, aided by the clamping action of the dryer fabric, the majority of the remaining water is evaporated.
So-called “triple-layer” or composite paper machine fabrics are known in the art. These generally include paper side and machine side warp and weft yarn systems, which are bound together by binder yarns.
The binder yarns may be disposed as single additional weft yarns with the exclusive function of binding the discrete fabric layers into a single composite structure. European Patent EP 0 269 070 to JWI, for example, shows such a structure. Because of the practical limitations in the frequency of bindings, between the binder yarns and the warp yarns of the paper side and wear side layers of composite structures with only a single binder yarn, there is a limit to the delamination resistance. Further, in this structure the binder yarns change from weaving above a paper side warp, to weaving below a wear side warp within the space of several warp yarns, such that undesirable basis weight variation may occur in the sheet.
From European Patent EP 1 000 197 binder yarns disposed in pairs are known. According to this document the binder yarns are “integrated” into the papermaking surface and so called integrated binder yarns. The binder yarns of each pair are interwoven with the top and bottom machine direction yarns such that, as a fiber support portion of the first binder yarn is interwoven with the top machine direction yarns, a binding portion of the second binder yarn is positioned below the top machine direction yarns and vice versa. Further, the first and second binder yarns cross each other as they pass below a transitional top machine direction yarn. Although the binder yarns are integrated into the papermaking surface, imperfections in the weave of the “integrated” binders sometimes impart wire marking on the paper sheet.